Cellulose resin composition and cellulose resin film

ABSTRACT

Provided are a cellulose resin composition and cellulose resin film which are free from the problem of bleeding even when containing a plasticizer in a relatively large amount. 
     The present invention relates to a cellulose resin composition obtained by adding (A) polyester plasticizer to a cellulose resin, wherein the aforementioned (A) polyester plasticizer is obtained by allowing a polybasic acid and a polyalcohol to react and 80 mol % or more of said polybasic acid is a succinic acid and an adipic acid. The present invention also relates to a cellulose resin film obtained from the cellulose-based resin composition.

TECHNICAL FIELD

The present invention relates to a cellulose resin composition andcellulose resin film. Particularly, the present invention relates to acellulose resin composition which is suitably used for a polarizingplate and protective film for polarizing plate, and a cellulose resinfilm which is obtained from the resin composition.

Compared to other synthetic resins, cellulose resins are mainlycharacterized by generally having a superior strength, transparency andgloss, as well as a smoother surface with excellent texture. Because ofthis, cellulose resins are used in a wide variety of applications, forexample, sheets, films, wire coatings, toys, medical instruments, foodpackaging materials and the like.

However, since cellulose resins are not thermoplastic, there has beenproblems in that these resins, when molding, have to be melted at a hightemperature or dissolved into a solvent, and that in cases where theyare melted at a high temperature, they are simultaneously thermallydecomposed and become colored. Therefore, in order to avoid suchproblems, it is necessary to blend an appropriate plasticizer whichlowers the softening point of the cellulose resin. Examples ofconventionally used plasticizer for this purpose include triphenylphosphate, tricresyl phosphate, diphenyl phosphate, triethyl phosphate,tributyl phosphate, dimethyl phthalate, diethyl phthalate,dimethoxyethyl phthalate, ethyl phthalyl ethyl glycolate, butyl phthalylbutyl glycolate, toluenesulfonamide, triacetin and pentaerythritoltetraacetate.

However, at present, none of the aforementioned plasticizers satisfies awide range of performances such as compatibility with cellulose resins,plasticizing efficiency, non-volatility, stability against heat andlight, non-migratory property, non-extractability and water resistance,and this is discouraging a further expansion of the use of celluloseresin compositions.

In view of this, a plasticizer having a hydrocarbon ring was proposed inPatent Document 1 and an ester compound of polyalcohol having differentalkyl groups and aryl groups was proposed in Patent Document 2.

In addition, recent years have seen the development in thinning andweight reduction of information devices equipped with a liquid crystaldisplay such as laptop computers. At the same time, the demands for eventhinner polarizing plate protective film used in liquid crystal displayshave increased.

Meanwhile, conventionally, cellulose triacetate films have been commonlyand widely used for a polarizing plate protective film, and aplasticizer has been added to such cellulose triacetate films in orderto improve the film flexibility and to reduce the moisture permeability.

However, there have been cases where simple thinning of theaforementioned cellulose triacetate film increased the moisturepermeability of the film and made it impossible to sufficiently reducethe moisture, thereby deteriorating the adhesive and polarizer when thefilm was made into a polarizing plate. As the solution to this problem,it can be considered to increase the amount of the plasticizer tocompensate the amount reduced by the thinning; however, a mere increasein the amount of the plasticizer does not enable a sufficientimprovement in the moisture permeability, and it has been found thatsuch an increase in the amount of the plasticizer causes new problems,such as deterioration in the retainability. Here, deterioration in theretainability refers to a property in which the film mass is decreasedby precipitation, evaporation and the like of the additive such asplasticizer to the outside of the film under a high temperature andhumid environment. This retainability is poor in conventional celluloseester films, resulting in a decrease in the performance of liquidcrystal displays.

In view of the above, as the technique to improve these defects, PatentDocument 3 proposes the use of citrate, while the use of pentaerythritolis proposed in Patent Document 4. In addition, Patent Document 5proposes the use of glyceride, while the use of diglycerol ester isproposed in Patent Document 6.

RELATED ART Patent Documents

-   Patent Document 1: Japanese Unexamined Patent Application    Publication No. 53-40039-   Patent Document 2: Japanese Unexamined Patent Application    Publication No. 54-71141-   Patent Document 3: Japanese Unexamined Patent Application    Publication No. 11-92574-   Patent Document 4: Japanese Unexamined Patent Application    Publication No. 11-124445-   Patent Document 5: Japanese Unexamined Patent Application    Publication No. 11-246704-   Patent Document 6: Japanese Unexamined Patent Application    Publication No. 2000-63560

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, the cellulose resin compositions according to Patent Documents1 and 2 have a problem with bleeding of plasticizer on the surface ofresin, and thereby these are not satisfactory. Further, the celluloseresin compositions according to Patent Documents 3 to 6 exhibitimproving effects on transparency and retainability, but there is a needfor more sufficient improvement with respect to bleeding of plasticizeron the resin surface in the case of blending plasticizer in largeamounts.

Therefore, an object of the present invention is to provide a celluloseresin composition and cellulose resin film which are free from theproblem of bleeding even when containing a plasticizer in a relativelylarge amount.

Means for Solving the Problems

In order to solve the aforementioned problems, the present inventorsintensively studied to discover that the aforementioned object can beattained by adding to cellulose resin a specific polyester plasticizerin which succinic acid and adipic acid are used as polybasic acidcomponent and stopper is not used.

That is, the cellulose resin composition according to the presentinvention is a cellulose resin composition, which is obtained by adding(A) polyester plasticizer to a cellulose resin, wherein theaforementioned polyester plasticizer is obtained by allowing a polybasicacid and a polyalcohol to react and 80 mol % or more of theaforementioned polybasic acid is a succinic acid and an adipic acid.

Additionally, in the cellulose resin composition according to thepresent invention, it is preferred that the molar ratio of the succinicacid and the adipic acid in the aforementioned polybasic acid is 80/20to 40/60.

Further, in the cellulose resin composition according to the presentinvention, it is preferred that the aforementioned (A) polyesterplasticizer is an oligoester having a weight average molecular weight of500 to 2000.

Furthermore, in the cellulose resin composition according to the presentinvention, it is preferred that the aforementioned (A) polyesterplasticizer is added in an amount of 3 to 50 parts by mass with respectto 100 parts by mass of the aforementioned cellulose resin.

Moreover, in the cellulose resin composition according to the presentinvention, it is preferred that the aforementioned cellulose resin iscellulose triacetate.

The cellulose resin film according to the present invention is obtainedfrom the aforementioned cellulose resin composition.

Effects of the Invention

According to the present invention, a cellulose resin composition whichis free from bleeding, takes advantage of excellent property ofplasticizer even when containing plasticizer in a relatively largeamount and is appropriately usable as liquid crystal display member suchas polarizing plate, protective film for polarizing plate, phase plates,reflective plates, viewing angle-improving films, antiglare films,non-reflective films and antistatic films, and a cellulose resin film inwhich the composition is used can be provided.

BEST MODE FOR CARRYING OUT THE INVENTION

The cellulose resin composition of the present invention will bedescribed in detail.

The cellulose resin used in the present invention is not particularlyrestricted; however, it preferably includes a lower fatty acid ester ofcellulose (hereinafter, also referred to as “cellulose ester”). Thelower fatty acid in the lower fatty acid ester of cellulose refers to afatty acid having not more than 6 carbon atoms. Examples of such lowerfatty acid esters of cellulose include cellulose acetate, cellulosepropionate, cellulose butyrate and the like, as well as mixed fatty acidesters such as cellulose acetate propionate and cellulose acetatebutyrate that are described in Japanese Unexamined Patent ApplicationPublication No. 10-45804, Japanese Unexamined Patent ApplicationPublication No. 8-231761, the Description of U.S. Pat. No. 2,319,052 andthe like. Among these lower fatty acid esters of cellulose, cellulosetriacetate is particularly preferably used.

With regard to such cellulose triacetate, from the standpoint of thefilm strength, those having a polymerization degree of 250 to 400 and anaverage acetylation degree (an amount of bound acetic acid) of 54.0% to62.5% are preferred, and those having an average acetylation degree of58.0% to 62.5% are more preferred.

A particularly preferred lower fatty acid ester of cellulose is acellulose ester which has a C₂ to C₄ acyl group as the substituent andsimultaneously satisfies the following formulae (I) and (II):2.6≦X+Y≦3.0,  Formula (I)and0≦X≦2.5,  Formula (II)

wherein, X represents the substitution degree of the acetyl group and Yrepresents the substitution degree of the propionyl group or butyrylgroup.

Further, it is especially preferred that the aforementioned lower fattyacid ester of cellulose be a cellulose acetate propionate. Among thecellulose acetate propionates, those satisfying 1.9≦X≦2.5 and 0.1≦Y≦0.9are more preferred. Those moieties which are not substituted with anacyl group generally exist as a hydroxyl group. These cellulose esterscan be synthesized by a known method.

Moreover, as the cellulose ester in the present invention, celluloseesters synthesized using raw material such as cotton linter, wood pulpor kenaf may be used individually or in combination. It is particularlypreferred to use a cellulose ester synthesized from cotton linter(hereinafter, may be simply referred to as linter) individually or incombination.

In the present invention, the (A) polyester plasticizer is obtained froma polybasic acid and a polyalcohol. As such polybasic acid, for example,aliphatic dibasic acids such as malonic acid, succinic acid, glutaricacid, adipic acid, sebacic acid, azelaic acid and dodecane dicarboxylicacid are used individually or in combination. In addition, a smallfraction of an aromatic polybasic acid, such as phthalic acid,isophthalic acid, terephthalic acid, trimellitic acid or pyromelliticacid, or an aliphatic polybasic acid, such as butane tricarboxylic acid,tricarballylic acid or citric acid, may also be used.

Additionally, in the present invention, 80 mol % or more, preferably 86%or more, more preferably 90 mol % or more of the polybasic acidcomponent is succinic acid and adipic acid. The molar ratio of theamount of succinic acid and adipic acid is preferably 80/20 to 40/60,particularly preferably 75/25 to 45/55. By using succinic acid andadipic acid in such amount ranges, the compatibility can be improvedconsiderably.

As the polyalcohol in the present invention, for example, aliphaticglycols such as ethylene glycol, diethylene glycol, 1,2-propanediol,1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol,2,2-diethyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, 1,5-pentanediol, 1,5-hexanediol, 1,6-hexanediol,3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol and2,2,4-trimethyl-1,3-pentanediol are used individually or in combination.In addition, a small fraction of polyalcohols such as glycerin,trimethylolpropane, trimethylolethane and pentaerythritol may also beused. Particularly, it is preferred that ethylene glycol is used as maincomponent, because a polyester plasticizer having excellentcompatibility can be obtained.

Further, in the present invention, it is preferred that (A) polyesterplasticizer is an oligoester having a weight average molecular weight of500 to 2000. Such range of weight average molecular weight of (A)polyester plasticizer makes the plasticizer less likely to bleed on theresin surface.

The aforementioned polyester plasticizer can be produced by a well-knownmethod, for example, by using the aforementioned polybasic acid and theaforementioned polyalcohol in the presence of a catalyst such asdibutyltin oxide or tetra-alkyl titanate. The ratio of eachaforementioned component used in the production varies depending on, forexample, the type of the component used, the desired characteristics ofthe polyester plasticizer and its molecular weight; however, in general,an aliphatic polybasic acid is used at a ratio of 10 to 80 mass %, whilea polyalcohol is used at a ratio of 10 to 80 mass %.

Suitable examples of the polyester plasticizer used in the presentinvention are concretely shown in Table 1 below. In Table 1, AV, OHV, Mwand the numbers in parentheses under the mixture names represent acidvalue, hydroxyl value, molecular weight and molar ratio, respectively.

TABLE 1 Polybasic acid Polyalcohol Stopper AV OHV Mw No. 1 Succinicacid/ Ethylene glycol — 0.3 112 1000 Adipic acid/ Sebacic acid(43/43/14) No. 2 Succinic acid/ Ethylene glycol — 0.3 114 1000 Adipicacid (70/30) No. 3 Succinic acid/ Ethylene glycol — 0.3 110 1000 Adipicacid (50/50) No. 4 Succinic acid/ Ethylene glycol — 0.3 115 1000 Adipicacid (30/70) No. 5 Succinic acid/ Ethylene glycol/ — 0.4 111 1000 Adipicacid Propylene glycol (70/30) (50/50) No. 6 Succinic acid/ Ethyleneglycol/ — 0.4 112 1000 Adipic acid Propylene glycol (50/50) (50/50)

Further, it is preferred that the acid value of the aforementionedpolyester plasticizer be not more than 1.

The amount of the aforementioned polyester plasticizer in the presentinvention is 3 to 50 parts by mass, preferably 5 to 30 parts by mass,with respect to 100 parts by mass of the cellulose resin. Theflexibility-imparting effect may not be attained when the amount is lessthan 3 parts by mass, and bleeding may occur when the amount exceeds 50parts by mass, which are not preferred.

Further, various additives, for example, phosphorous antioxidant,phenolic antioxidant or sulfur antioxidant, ultraviolet absorbing agent,hindered amine light stabilizer and the like may also be blended in thecellulose resin composition of the present invention.

Examples of the aforementioned phosphorous antioxidant include triphenylphosphite, tris(2,4-di-tert-butylphenyl)phosphite,tris(nonylphenyl)phosphite, tris(dinonylphenyl)phosphite, tris(mono-,di-mixed nonylphenyl)phosphite,bis(2-tert-butyl-4,6-dimethylphenyl)-ethyl phosphite, diphenyl acidphosphite, 2,2′-methylene-bis(4,6-di-tert-butylphenyl)octyl phosphite,diphenyldecyl phosphite, phenyldiisodecyl phosphite, tributyl phosphite,tris(2-ethylhexyl)phosphite, tridecyl phosphite, trilauryl phosphite,dibutyl acid phosphite, dilauryl acid phosphite, trilauryl trithiophosphite, bis(neopenthyl glycol).1,4-cyclohexanedimethyl diphosphite,bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite,bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite,distearyl pentaerythritol diphosphite, phenyl-4,4′-isopropylidenediphenol.pentaerythritol diphosphite, tetra(C12-C15 mixedalkyl)-4,4′-isopropylidene diphenyl phosphite,bis[2,2′-methylene-bis(4,6-diamylphenyl)].isopropylidene diphenylphosphite, hydrogenated-4,4′-isopropylidene diphenol polyphosphite,bis(octylphenyl).bis[4,4′-n-butylidene-bis(2-tert-butyl-5-methylphenol)].1,6-hexanediol.diphosphite,tetramidecyl.4,4′-butylidene-bis(2-tert-butyl-5-methylphenol)diphosphite,hexa(tridecyl).1,1,3-tris(2-methyl-5-tert-butyl-4-hydroxyphenyl)butane.triphosphonite,9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and2-butyl-2-ethyl-propanediol.2,4,6-tri-tert-butylphenol monophosphite.

Examples of the aforementioned phenolic antioxidant include2,6-di-tert-butyl-p-cresol, 2,6-diphenyl-4-octadecyloxyphenol,stearyl(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,distearyl(3,5-di-tert-butyl-4-hydroxybenzyl) phosphonate,tridecyl.3,5-di-tert-butyl-4-hydroxybenzyl thioacetate,thiodiethylene-bis[(3,5-di-tert-butyl-4-hydroxyphenyl) propionate],4,4′-thiobis(6-tert-butyl-m-cresol),2-octylthio-4,6-di(3,5-di-tert-butyl-4-hydroxyphenoxy)-s-triazine,2,2′-methylene-bis(4-methyl-6-tert-butylphenol),bis[3,3-bis(4-hydroxy-3-tert-butylphenyl)butyric acid]glycol ester,4,4′-butylidene-bis(4,6-di-tert-butylphenol),2,2′-ethylidene-bis(4,6-di-tert-butylphenol),1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,bis[2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl]terephthalate,1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate,1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate,1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene,1,3,5-tris[(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxyethyl]isocyanurate,tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane,2-tert-butyl-4-methyl-6-(2-acryloyloxy-3-tert-butyl-5-methylbenzyl)phenol,3,9-bis[2-(3-tert-butyl-4-hydroxy-5-methylhydrocinnamoyloxy)-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane]and triethyleneglycol-bis[β-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate].

Examples of the aforementioned sulfur antioxidant include dialkylthiodipropionates, such as dilauryl thiodipropionate, dimyristylthiodipropionate, myristylstearyl thiodipropionate and distearylthiodipropionate, and β-alkylmercaptopropionates of polyols such aspentaerythritol tetra(β-dodecylmercaptopropionate).

Examples of the aforementioned ultraviolet absorbing agent include2-hydroxybenzophenones such as 2,4-dihydroxybenzophenone,2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone,2-hydroxy-4-tert-butyl-4′-(2-methacryloyloxyethoxyethoxy)benzophenoneand 5,5′-methylene-bis(2-hydroxy-4-methoxybenzophenone);2-(2-hydroxyphenyl)benzotriazoles such as2-(2-hydroxy-5-methylphenyl)benzotriazole,2-(2-hydroxy-5-tert-octylphenyl)benzotriazole,2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole,2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole,2-(2-hydroxy-3-dodecyl-5-methylphenyl)benzotriazole,2-(2-hydroxy-3-tert-butyl-5-C7 to C9mixed-alkoxycarbonylethylphenyl)triazole,2-(2-hydroxy-3,5-dicumylphenyl)benzotriazole,2,2′-methylene-bis(4-tert-octyl-6-benzotriazolylphenol) and polyethyleneglycol ester of 2-(2-hydroxy-3-tert-butyl-5-carboxyphenyl)benzotriazole;2-(2-hydroxyphenyl)-1,3,5-triazines such as2-(2-hydroxy-4-hexyloxyphenyl)-4,6-diphenyl-1,3,5-triazine,2-(2-hydroxy-4-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine,2-(2-hydroxy-4-octoxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazineand2-(2-hydroxy-4-acryloyloxyethoxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine;benzoates such as phenyl salicylate, resorcinol monobenzoate,2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate,2,4-di-tert-amylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate andhexadecyl-3,5-di-tert-butyl-4-hydroxybenzoate; substituted oxanilidessuch as 2-ethyl-2′-ethoxyoxanilide and 2-ethoxy-4′-dodecyloxanilide; andcyanoacrylates such as ethyl-α-cyano-β,β-diphenylacrylate andmethyl-2-cyano-3-methyl-3-(p-methoxyphenyl)acrylate.

Examples of the aforementioned hindered amine light stabilizer include2,2,6,6-tetramethyl-4-piperidylstearate,1,2,2,6,6-pentamethyl-4-piperidylstearate,2,2,6,6-tetramethyl-4-piperidylbenzoate,bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate,bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate,bis(1-octoxy-2,2,6,6-tetramethyl-4-piperidyl)sebacate,tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate,tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate,bis(2,2,6,6-tetramethyl-4-piperidyl).bis(tridecyl)-1,2,3,4-butanetetracarboxylate,bis(1,2,2,6,6-pentamethyl-4-piperidyl).bis(tridecyl)-1,2,3,4-butanetetracarboxylate,bis(1,2,2,6,6-pentamethyl-4-piperidyl)-2-butyl-2-(3,5-di-tert-butyl-4-hydroxybenzyl)malonate, 1-(2-hydroxyethyl)-2,2,6,6-tetramethyl-4-piperidinol/diethylsuccinate polycondensate,1,6-bis(2,2,6,6-tetramethyl-4-piperidylamino)hexane/dibromoethanepolycondensate,1,6-bis(2,2,6,6-tetramethyl-4-piperidylamino)hexane/2,4-dichloro-6-morpholino-s-triazinepolycondensate,1,6-bis(2,2,6,6-tetramethyl-4-piperidylamino)hexaxne/2,4-dichloro-6-tert-octylamino-s-triazinepolycondensate,1,5,8,12-tetrakis[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidyl)amino)-s-triazine-6-yl]-1,5,8,12-tetraazadodecane,1,5,8,12-tetrakis[2,4-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino)-s-triazine-6-yl]-1,5,8,12-tetraazadodecane,1,6,11-tris[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidyl)amino)-s-triazine-6-ylamino]undecane,1,6,11-tris[2,4-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino)-s-triazine-6-ylamino]undecane,3,9-bis[1,1-dimethyl-2-{tris(2,2,6,6-tetramethyl-4-piperidyloxycarbonyloxy)butylcarbonyloxy}ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane,and 3,9-bis[1,1-dimethyl-2-{tris(1,2,2,6,6-pentamethyl-4-piperidyloxycarbonyloxy)butylcarbonyloxy}ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane.

In addition to the above, as required, other additives may be blendedwith the cellulose resin composition of the present invention, andexamples thereof include fillers, coloring agents, cross-linking agents,antistatic agents, anti-plate-out agents, surface treatment agents,lubricants, flame retardants, fluorescent agents, antifungal agents,antibacterial agents, metal inactivators, releasing agents, pigments,processing aids, antioxidants, light stabilizers and foaming agents.

The cellulose resin composition of the present invention can be used ina variety of applications by various known processing methods; however,because of the characteristics thereof, it is preferably usedparticularly as a cellulose resin film such as polarizing plate orprotective film for polarizing plate.

The cellulose resin film of the present invention is obtained from theaforementioned cellulose resin composition. Next, a method of producinga cellulose ester film which comprises the cellulose resin composition(hereinafter, may be referred to as “the cellulose ester film of thepresent invention”) will be explained.

The cellulose ester film of the present invention is produced byapplying and drying a dope solution in which a cellulose ester isdissolved in a solvent. Various additives may be added to the dopesolution as required. The concentration of the cellulose ester in thedope solution is preferably high since it enables a reduction in thedrying load after flow-casting the dope solution onto a substrate;however, when the concentration of the cellulose ester is too high, thefiltering load is increased, thereby lowering the filtration accuracy.In order to attain reduction in both the drying load and filtering load,the concentration of the cellulose ester is preferably 10 to 30 mass %,more preferably 15 to 25 mass %.

The solvent for the preparation of the dope solution of the presentinvention may be used individually or in combination with anothersolvent; however, from the standpoint of the production efficiency, itis preferred to use a good solvent and poor solvent of cellulose esterin combination. Preferred ranges of the mixing ratio of the good solventand poor solvent are 70 to 98 mass % for the good solvent and 30 to 2mass % for the poor solvent. With regard to the good solvent and poorsolvent used in the present invention, a solvent which independentlydissolves the cellulose ester used is defined as a good solvent, while asolvent which, by itself, can only swell the cellulose ester used orcannot dissolve the cellulose ester used, is defined as a poor solvent.Therefore, the good solvent and poor solvent are variable depending onthe average acetylation degree of cellulose. For example, acetone is agood solvent for cellulose esters having an average acetylation degreeof 55%, while it is a poor solvent for cellulose esters having anaverage acetylation degree of 60%.

As clearly seen from the explanation in the above, the good solvent andpoor solvent are not unambiguously determined in all cases; however, incases where the cellulose resin is cellulose triacetate, organichalogenated compounds such as methylene chloride and dioxolanes areexemplified as good solvent used in the present invention. In caseswhere the cellulose resin is cellulose acetate propionate, methylenechloride, acetone, methyl acetate and the like are exemplified as thegood solvent, while examples of poor solvent include methanol, ethanol,n-butanol, cyclohexane and cyclohexanone.

A conventional method can be used as the method of dissolving celluloseester in the preparation of the aforementioned dope solution; however,it is preferred to employ a method in which cellulose ester is dissolvedwith stirring by heating in a temperature range which is not lower thanthe boiling point of the solvent under atmospheric pressure and wherethe solvent does not boil, since such method prevents generation ofaggregated non-dissolved matter called gel or lump. Further, a method inwhich cellulose ester is mixed with a poor solvent to wet or swell thecellulose ester followed by dissolution thereof by further mixing with agood solvent is also preferably employed. Furthermore, a known coolingdissolution method may also be employed. In cases where a coolingdissolution method is employed, methyl acetate or acetone may be used asthe good solvent. Pressurization can be carried out by a method ofinjecting inert gas such as nitrogen gas or by increasing the vaporpressure of the solvent by heating. It is preferred that the heating bedone externally. For example, a jacket-type heater is preferably usedsince the temperature control is easy.

From the standpoint of the solubility of cellulose esters, as theheating temperature after the addition of solvent, a temperature rangewhich is not lower than the boiling point of the solvent used underatmospheric pressure and where the solvent does not boil is preferred;however, when the heating temperature is too high, the required pressureis increased, thereby lowering the productivity. The heating temperaturerange is preferably 45 to 120° C., more preferably 60 to 110° C., stillmore preferably 70 to 105° C. Further, the pressure is adjusted in sucha manner that the solvent does not boil at the preset temperature.

Next, this cellulose ester solution is filtered using an appropriatefilter medium such as filter paper. As the filter medium, a filterhaving a small absolute filtration accuracy is preferred in order toremove undesired matters and the like; however, an excessively smallabsolute filtration accuracy leads to a problem that clogging of thefilter medium is likely to occur. In view of this, the absolutefiltration accuracy of the filter medium is preferably not greater than0.008 mm, more preferably in the range of 0.001 to 0.008 mm, still morepreferably in the range of 0.003 to 0.006 mm. The material of the filtermedium is not particularly restricted and any conventional material maybe used; however, filter media made of plastic such as polypropylene orTeflon (Registered Trademark) and those made of metal such as stainlessmetal are preferred since they do not cause fiber fall-off or the like.

The filtration of dope solution can be carried out by a conventionalmethod; however, it is preferred to employ a method in which the dopesolution is filtered under pressure while being heated at a temperaturerange which is not lower than the boiling point of the solvent usedunder atmospheric pressure and where the solvent does not boil, sincesuch method achieves only a small increase in the difference between thepressures on each side of the filter medium (hereinafter, may bereferred to as filtration pressure). The filtration temperature ispreferably 45 to 120° C., more preferably 45 to 70° C., still morepreferably 45 to 55° C. A smaller filtration pressure is preferred. Thefiltration pressure is preferably not higher than 1.6×10⁶ Pa, morepreferably not higher than 1.2×10⁶ Pa, still more preferably not higherthan 1.0×10⁶ Pa.

As the substrate used in the flow-casting (casting) step, those ofmirror-finished stainless steel in the shape of an endless belt or drumare preferred. It is preferred that the temperature of the substrateused in the casting step be 0° C. to below the boiling point of thesolvent. A higher temperature enables a faster drying speed; however, anexcessively high temperature may cause foaming and deteriorate theflatness of the substrate surface. The substrate temperature ispreferably 0 to 50° C., more preferably 5 to 30° C. The method tocontrol the substrate temperature is not particularly restricted;however, a method in which warm air or cool air is blown onto thesubstrate or a method in which a warm-water vat is brought into contactwith the substrate may be employed. Among these two methods, the methodof using a warm-water vat is more preferable since the heat transfer ismore efficient and the time required to bring the substrate temperatureconstant is shorter. In cases where warm air is used, it is necessarythat the temperature of the air be higher than the target temperature.In order to allow the cellulose ester film to exhibit a good surfaceflatness, the amount of remaining solvent at the time of film removalfrom the substrate is preferably 10 to 120%, more preferably 20 to 40%or 60 to 120%, and especially preferably 20 to 30% or 70 to 115%.

In the present invention, the amount of remaining solvent is defined bythe following formula:The amount of remaining solvent=[(film mass before heat treatment−filmmass after heat treatment)/(film mass after heat treatment)]×100(%).Here, the heat treatment in the measurement of the amount of remainingsolvent refers to heating of the film at 115° C. for 1 hour. Further, inthe step of drying the cellulose ester film, the film removed from thesubstrate is further dried in such a manner the amount of remainingsolvent becomes preferably not more than 3 mass %, more preferably notmore than 0.5 mass %. Generally employed in the film drying step is amethod in which the film is dried while being carried by a rollsuspension method or tenter method.

Further, it is preferred that the maintenance of the film width and filmdrawing be carried out by a tenter method while a large amount ofsolvent still remains immediately after removing the film from thesubstrate, since this enables the film to demonstrate a superiordimensional stability improving effect. The means for drying the film isnot particularly restricted, and it is carried out with hot air,infrared radiation, heating roller, microwave or the like. It ispreferred to use hot air from the standpoint of simplicity. It ispreferred that the drying temperature be stepwisely increased in therange of 40 to 150° C., and in order to improve the dimensionalstability, it is more preferred that the drying be carried out at atemperature of 50 to 140° C.

It is preferred that the cellulose ester film have a less thicknesssince the resulting polarizing plate would be thinner and thus thethinning of liquid crystal display would be easier; however, anexcessively thin cellulose ester film leads to an increase in themoisture permeability, thereby making the tearing strength and the likeinsufficient. In order to attain both low moisture permeability andsufficient tearing strength, the thickness of the cellulose ester filmis preferably 10 to 65 μm, more preferably 20 to 60 μm, still morepreferably 35 to 50 μm.

Since the cellulose ester film of the present invention can attain a lowmoisture permeability and high dimensional stability and the like, it ispreferably used as a liquid crystal display member. A liquid crystaldisplay member refers to a member used in a liquid crystal displaydevice and examples thereof include polarizing plate, protective filmfor polarizing plate, phase plates, reflective plates, viewingangle-improving films, antiglare films, non-reflective films, antistaticfilms and the like. Thereamong, the cellulose ester film of the presentinvention is preferably used for a polarizing plate and protective filmfor polarizing plate.

The polarizing plate can be produced by a conventional method. Forexample, there is a method in which the cellulose ester film of thepresent invention is subjected to an alkaline saponification treatmentand subsequently, using a completely saponificated polyvinyl alcoholsolution, the resultant is pasted onto both sides of a polarizing filmproduced by immersion in an iodine solution and drawing therefrom. Thealkaline saponification treatment refers to a treatment in whichcellulose ester film is immersed in a hot strong alkaline solution inorder to improve the wetting of water-based adhesive and its adhesiveproperty.

The smaller the retardation Ro (nm) in the film plane direction of theaforementioned cellulose ester film, the more preferable it is. Theretardation Ro (nm) is preferably not greater than 100 nm, morepreferably not greater than 10 nm, and still more preferably not greaterthan 5 nm. In cases where the cellulose ester film of the presentinvention is used as a retarder film, the Ro (nm) thereof is preferably50 to 1,000 nm. As for the determination of the retardation Ro, thethree-dimensional refractive index of the cellulose ester film at awavelength of 590 nm is measured using an automatic double refractometerto determine the retardation axis angle θ₁ and refractive indices Nx andNy, and the retardation Ro in the film plane direction is thencalculated according to the following formula:Ro=(Nx−Ny)×d.In this formula, Nx, Ny and d represent, respectively, the filmrefractive index in the direction parallel to the film-formingdirection, the film refractive index in the direction perpendicular tothe film-forming direction, and the film thickness (nm).

In cases where the cellulose ester film of the present invention is usedas an optical film, the closer the angle θ₀ between the film-formingdirection (this corresponds to the film longitudinal direction) and thefilm retardation axis is to 0°, +90° or −90°, the more preferable it is.The angle θ_(p) contributes to an improvement of the degree ofpolarization of the resulting polarizing plate, especially when thecellulose ester film of the present invention is used as a protectivefilm for polarizing plate. Here, the retardation axis means thedirection in which the refractive index in the film surface is thehighest. Further, it is preferred that the θ₁ (radian) (θ₁ is obtainedby converting the θ₀ into a radian expression) and the retardation R_(o)in the film plane direction satisfy the relation represented by thefollowing formula:p≦1−sin²(2θ₁)−sin²(πR _(o)/λ).The p is preferably not less than 0.99900, more preferably not less than0.99990, still more preferably not less than 0.99995, and especiallypreferably not less than 0.99999. The λ represents the wavelength (nm)of the light, which is in the range of 380 to 650 nm, used in themeasurement of the three-dimensional refractive-index for determiningthe Ro and θ₁. The above formula is satisfied preferably when λ is 590nm, more preferably when λ is 400 nm.

EXAMPLES

The cellulose resin composition of the present invention will bedescribed in more detail by way of Examples; however, the presentinvention is not limited thereto.

Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-5

Acetylcellulose (produced by Daicel Chemical Industries, Ltd; LT-35) wasdissolved with stirring into a solvent comprising 100 parts by mass ofmethylene chloride to obtain a solution having a concentration of 15%.Mixed therewith was the plasticizer according to Table 2 below at anamount of 30 mass % with respect to the acetylcellulose, and the thusobtained solution was flow-casted onto a metal substrate to produce afilm having a thickness of approximately 0.1 mm. It should be noted herethat the plasticizers Nos. 1 to 6 in Table 2 correspond to those inTable 1 and that the plasticizers Nos. A to E correspond to those inTable 3 below. Further, in Table 3, AV, OHV, Mw and the numbers inparentheses under the mixtures represent acid value, hydroxyl value,molecular weight and molar ratio, respectively.

Next, using the thus obtained films (samples), performance testdescribed in the following was carried out. The results thereof aretogether shown in Table 2 below.

(Evaluation of Bleeding)

The samples were cut into a size of 10 cm×10 cm, left to stand for a dayat 23° C. and 55% RH (relative humidity), and then left to stand for 2weeks under a condition of 80° C. and 90% RH. The thus cut samples werefurther left to stand for a day at 23° C. and 55% RH and thereafter, thebleeding on the sample surface was visually observed. The evaluation wascarried out in accordance with the three criteria in the following.

∘ no bleeding and no change of film

Δ; no bleeding, but cloud in film

X; bleeding

TABLE 2 Plasticizer Bleeding Example 1-1 No. 1 Δ Example 1-2 No. 2 ◯Example 1-3 No. 3 ◯ Example 1-4 No. 4 Δ Example 1-5 No. 5 ◯ Example 1-6No. 6 ◯ Comparative No. A X Example 1-1 Comparative No. B X Example 1-2Comparative No. C X Example 1-3 Comparative No. D X Example 1-4Comparative No. E X Example 1-5

TABLE 3 Polybasic acid Polyalcohol Stopper AV OHV Mw No. A Succinic acidEthylene — 0.3 110 1000 glycol No. B Adipic acid Ethylene — 0.4 115 1000glycol No. C Succinic acid/ Ethylene 2-ethyl 0.3   6 1000 Adipic acidglycol hexanol (70/30) No. D Succinic acid/ Ethylene 2-ethyl 0.5   71000 Adipic acid glycol hexylic (70/30) acid Succinic acid/ No. E Adipicacid/ Ethylene — 0.3 114 1000 Sebacic acid glycol (35/35/30)

In the case of the use of polyester plasticizer obtained from polybasicacid and polyalcohol alone, when used only succinic acid as polybasicacid (Comparative Example 1-1) or when used only adipic acid aspolybasic acid (Comparative Example 1-2), bleeding occurred. Even in thecase of the use of polyester plasticizer obtained from the combinationof succinic acid and adipic acid as polybasic acid, when used 2-ethylhexanol as stopper (Comparative Example 1-3) or when used 2-ethylhexylic acid as stopper (Comparative Example 1-4), bleeding occurred.Further, in the case that the ratio of succinic acid and adipic acid islower than 80 mol % in polybasic acid (Comparative Example 1-5),bleeding occurred. In contrast, when used polyester plasticizer whichobtained from polybasic acid and polyalcohol alone and in which theratio of succinic acid and adipic acid is 80 mol % or more in polybasicacid (Examples 1-1 to 1-6), bleeding did not occur.

The invention claimed is:
 1. A cellulose resin composition, which isobtained by adding (A) polyester plasticizer to a cellulose resin,wherein said (A) polyester plasticizer is obtained by allowing polybasicacids and at least one polyalcohol to react and 80 mol % or more of saidpolybasic acids are a succinic acid and an adipic acid, and wherein themolar ratio of said succinic acid and said adipic acid in said at leastone polybasic acids is 80/20 to 40/60.
 2. The cellulose resincomposition according to claim 1, wherein said (A) polyester plasticizeris an oligoester having a weight average molecular weight of 500 to2000.
 3. The cellulose resin composition according to claim 1, whereinsaid (A) polyester plasticizer is added in an amount of 3 to 50 parts bymass with respect to 100 parts by mass of said cellulose resin.
 4. Thecellulose resin composition according to claim 1, wherein said celluloseresin is cellulose triacetate.
 5. A cellulose resin film, which isobtained from the cellulose resin composition according to claim 1.